Electric vacuum cleaner

ABSTRACT

An electric vacuum cleaner includes a filter, blower, switching element for switching current flowing through the blower, current detecting section, and control section, wherein the control section includes a first control mode in which an amount of airflow flowing through the filter and the blower is restrained and a second control mode in which an applied power to the blower is maintained to a target value, and selects one of the first and second control modes according to the applied power.

CROSS REFERENCE OF THE INVENTION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-064330 filed on Mar. 8, 2005, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates generally to an electric vacuum cleaner, and more particularly to a controller controlling operation of a blower provided to the electric vacuum cleaner.

(2) Description of the Related Art

An electric vacuum cleaner has a blower generating an air-flow containing dust and a filter which separates the dust from the air-flow and collects the dust. Increasing the amount of collected dust causes air-flow resistance in an intake side of the blower to increase and the air-flow to decrease, resulting in reducing the suction power by the blower in the cleaner if the applied power is constant. An operator or user generally desires that an electric vacuum cleaner can have a stable suction power generating an air-flow irrespective of an amount of collected or trapped dust in the filter.

In connection with this, the Japanese Laid-open (Kokai) Patent No. HEI 08-228978 discloses an electric vacuum cleaner configured to compare a current varying depending on air-flow resistance in an intake side of a blower, i.e., current flowing through the blower, with a prescribed threshold value, and vary in rise and/or descent the applied power to the blower step by step in response to the compared result, repeatedly.

In a household electric vacuum cleaner, an upper limit value is applied to an input power for the sake of energy saving and it is occasionally required under some circumstance to have a high suction power generating air-flow within an input power range not exceeding the upper limit value.

Conventionally, an electric vacuum cleaner has been configured to compare a current flowing through a blower with a prescribed threshold value and to control the input power to the blower to be increased or decreased step by step to vary an amount of air-flow drawing through the blower in response to the compared result. In case that an applied power is controlled to become a target value using the conventional method, it is required beforehand to prepare a lot of current threshold values to smoothly adjust the applied power to the target value and thus a memory having a large storage capacity is needed. In addition, a lot of experiments are also needed to determine such a large amount of current threshold values and thus, development efficiency of a controller is deteriorated.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an electric vacuum cleaner implementing two different controls, one of which is to maintain a suitable amount of air flow irrespective of increasing an amount of collected dust on a filter and the other is to adjust an applied power to a target value.

To accomplish the above object, an electric vacuum cleaner comprising:

a blower for generating an air flow containing dust;

a filter configured to separate dust from the air flow;

a switching element for switching a current flowing through the blower in response to a control signal;

an air-flow-amount sensing section for sensing an amount of the air flowing through the filter to output a first value indicating the sensed result, the air-flow-amount being varied in response to amount of the dust separated by the filter;

a current detecting section for detecting a current flowing through the blower to output a second value indicating the detected current value; and

a control section for selecting, in accordance with power applied to the blower, one of a first control mode in which a suitable output timing of the control signal from the control section to the switching element is determined so that variation of the amount of the air flow is restrained based on the first value and a second control mode in which a suitable output timing of the control signal is determined so that the applied power to the blower is maintained at a prescribed target value based on the second value and for controlling the operation of the switching element with the control signal outputted at the suitable output timing of the selected mode.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention will become apparent and more readily appreciated from the following detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view showing an electric vacuum cleaner according to an embodiment of the present invention;

FIG. 2 is a block diagram illustrating a controller of an electric vacuum cleaner according to a first embodiment of the present invention;

FIG. 3 is a view illustrating a voltage waveform, a current waveform, and a signal waveform from respective sections according to the first embodiment;

FIG. 4 is a block diagram showing function of the respective sections of a controller in the first embodiment;

FIG. 5 is a view of a data table for the first embodiment;

FIG. 6 is a graph illustrating a relationship between an intake-air-flow amount and an applied power of a blower when the electric vacuum cleaner in the first embodiment is driven;

FIG. 7 is a flow chart illustrating a process in which control modes are switched by a microprocessor in the first embodiment;

FIG. 8 is a block diagram showing function of the respective sections of a controller in a second embodiment;

FIG. 9 is a block diagram illustrating a controller of an electric vacuum cleaner according to a third embodiment;

FIG. 10 a view illustrating a voltage waveform and a signal waveform from respective sections according to the third embodiment;

FIG. 11 is a block diagram showing function of the respective sections of a controller in the third embodiment;

FIG. 12 is a graph illustrating a relationship between both an intake-air-flow amount and an applied power of a blower when the electric vacuum cleaner in a fourth embodiment is driven;

FIG. 13 is a block diagram illustrating a controller of an electric vacuum cleaner according to a fifth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in more detail with reference to the accompanying drawings. However, the same numerals are applied to the similar elements in the drawings, and therefore, the detailed descriptions thereof are not repeated.

FIRST EMBODIMENT

Firstly, structure of a canister type electric vacuum cleaner 20 (hereinafter referred to as a “cleaner 20”) will now be described with reference to FIG. 1.

As shown in FIG. 1, a main body 21 of cleaner 20 includes a lower case 22 whose upper surface is open, an upper case 23, a bumper 24 and a lid 25. The rear top part of lower case 22 is closed by upper case 23. Bumper 24 is sandwiched between circumferential edges of lower case 22 and upper case 23 and is joined therewith. Lid 25 is swingably provided to the front part of lower case 22 to open and close the front part. Formed on the lid 25 is an informing section 40, including a light emitting element or a sounding element, e.g., a light Emitting Diode (LED) or speaker, to inform an operator of an operational state of the cleaner 20, e.g., an amount of collected dust, during its operation.

A bag-shaped filter 27 (hereinafter referred to as “filter 27”) and a blower 26 in a rear side of filter 27 are serially located in main body of cleaner 20. An airflow generated by blower 26 is led through filter 27 to separate dust from the airflow.

A caster (not shown) is rotatably provided on a lower part of front side of main body 21 in a forwarding direction. A pair of idle wheels each having a large diameter is provided on both sides of rear side of main body 21.

An intake opening 29 is formed at a center of the front wall of main body 21 to draw air from the outside into the inside of main body 21. One end of a flexible cylindrical hose 30 is separably connected in fluid communication with intake opening 29 and the other end is fixed in fluid communication with an operational section 31.

Operational section 31 includes a plurality of operation buttons 32 each of which is selectively operated to instruct one of operation modes of blower 26 including strong, week, and “Off” modes. Operational section 31 further includes a handhold portion 33 which is grasped by an operator when cleaning. One end of an extendable pipe 34 is separably connected to a tip of operational section 31 so that extendable pipe 34 fluidly communicates with cylindrical hose 30 through operational section 31. Extendable pipe 34 includes a first pipe 34 a having a larger diameter and a second pipe 34 b having a smaller diameter which is slidably inserted into first pipe 34 a. Pipe 34 is extended by sliding second pipe 34 b against first pipe 34 a. A floor brush 35 having an opening through which dust on the floor is taken with airflow into cleaner 20 is separably connected to the other end of extendable pipe 34.

Serial connection arrangement of floor brush 35, extendable pipe 34, hose 30 forms a main airflow channel.

A controller 100 of cleaner 20 including blower 26 and a control section 10 a will now be described with reference to FIG. 2. In the inside of main body 21, blower 26 and a circuit board 101 on which a control section 10 a is functionally realized to control blower 26 is mounted.

Serially connected in controller 100 are a commercial AC power source 1, a current fuse 4, a motor 5 consisting in blower 26, and a switching element, e.g., bi-directional thyristor 2, which switches applied power from the AC power source 1 to blower 26.

Blower 26 essentially comprises motor 5 and a fan 13. Motor 5 is of a universal type, e.g., a commutator motor (brush motor), which comprises an armature 5 a with a commutator and field windings 5 b, 5 c. Fan 13 is of a centrifugal type fixed to a spindle of motor 5.

A current detecting section 3 is provided to controller 100. Current detecting section 3 is comprised of, for example, a current-transformer or a shunt-resistance to detect a load current flowing through motor 5. Since current flowing through motor 5 varies in response to an amount of airflow passing through filter 27, the amount of the airflow can be determined indirectly by detecting the current. In this embodiment, current detecting section 3 also serves as or is, so to say, an airflow amount sensing section. A zero-crossing point of AC voltage applied to motor 5 is detected by a zero-cross detecting section 6.

Control section 10 a includes a microprocessor 7, a memory 8, and an I/O port 9. I/O port 9 is equipped with an A/D conversion function. In memory 8, a control program for functionally operating microprocessor 7 and data including several constants needed to carry out operations by microprocessor 7 are stored beforehand. Memory 8 includes a data area for temporarily storing data from microprocessor 7 and a work area for microprocessor 7.

A detected current by current detecting section 3 is fed to I/O port 9 after being full-wave-rectified or half-wave-rectified by a rectifier 11. I/O port 9 includes analog to digital converter (A/D converter) converting an analog value into a digital value. While the rectified detected current is converted by the A/D converter, I/O port 9 acquires the digital value corresponding to the rectified detected current. A zero-cross detection signal generated by zero-cross detecting section 6 is also input to I/O port 9 when the zero-cross detecting section 6 detects the zero-cross point of AC voltage.

Controller 100 also includes operational section 31 from which an instruction signal 1 is output to I/O port 9.

Control section 10 a provided in controller 100 acquires the detected current value, i.e., current flowing through motor 5, the zero-cross detection signal, and the instruction signal, and then outputs a control signal to a gate terminal (a control terminal) of bi-directional thyristor 2.

When a power voltage having a waveform indicated in (a) of FIG. 3 from a commercial AC power source 1 is applied to controller 100 and the control signal from control section 10 a is applied to the gate terminal of bi-directional thyristor 2 at timings shown in (c) of FIG. 3, voltage shown in (d) of FIG. 3 is generated between terminals of motor 5 because bi-directional thyristor 2 short-circuits until a polarity of the power voltage is inverted.

At this time, the zero-cross detection signal indicated in (b) of FIG. 3 is input to I/O port 9 of control section 10 a. A waveform of current flowing through motor 5 which is detected by current detecting section 3 and full-wave-rectified by rectifier 11 is shown in (e) of FIG. 3. This current waveform is input as a voltage value to control section 10 a as it is or as a flattened waveform.

A conducting angle Φ (%) of bi-directional thyristor 2 is calculated by the following formula: Φ={(Tv/2)-ta}/(Tv/2)×100 wherein Tv (sec) is a period of AC power voltage, and ta (sec) is a time until the control signal of motor 5 is output after the AC power voltage comes to a zero-cross point. Hereinafter, the time ta (sec) is referred to as an output timing.

Each function implemented by control section 10 a is described with reference to FIG. 4. Control section 10 a generally includes a current acquiring section 71, a control mode selecting section 73 for selecting one of two control modes, e.g., a first control mode and a second control mode, and an output timing determination section 54 for determining the output timing ta.

Current acquiring section 71 repeatedly acquires a value In of current flowing through motor 5 (hereinafter referred to as “current In”) detected by current detecting section 3 at a predetermined period, and transfers the current In to control mode selecting section 73 and output timing determination section 54. Since current In against an applied power varies depending on a characteristic of blower 26 and the conducting angle Φ, it is required to experimentally determine the current In at a designing stage. An applied power under a constant power voltage can be estimated from current In. Control mode selecting section 73 selects one of the control modes of control section 10 a corresponding to the applied power to blower 26 based on current In. Output timing determination section 54 determines an output timing of the control signal to bi-directional thyristor based on the current In and the selected current mode by control mode selecting section 73.

As set forth above, control section 10 a selects one of the predetermined control modes based on the current In of blower 26, determines the output timing ta, and outputs the control signal according to this output timing ta. The output timing ta is used as an instruction value to switch on or off bi-directional thyristor 2.

The first and second control modes are now described. In the first control mode, blower 26 is controlled to restrain variation of an amount of airflow generated by blower 26 passing through filter 27. In the second control mode, an applied power to blower 26 is controlled to be adjusted to a prescribed target value. The control section 10 a selects one of the above-described first and second control modes.

Firstly, the first control mode is described in more detail. Data table 16 used in the first control mode is stored in memory 8, previously. Content of data table 16 is shown in FIG. 5. In this mode, current detecting section 3 functions as airflow amount sensing section.

Data table 16 includes n preset values of U1, U2, U3, - - - , and Un (Un< - - - <U<U2<U1) as respective output timing values at which a control signal is output to bi-directional thyristor 2. Data table 16 further includes a lower limited current threshold Ig1 and a higher limited current threshold Ig2. The lower limited current threshold Ig1 has n thresholds of X1, X2, X3, - - - , and Xn, (Xn> - - - >X3>X2>X1) each of which corresponds to each of the n preset values. The higher limited current threshold Ig2 also has n−1 thresholds of Y1, Y2, Y3, - - - , and Yn−1, (Yn−1> - - - >Y3>Y2>Y1) each of which corresponds to each of the n preset values. As shown in FIG. 6, each of the lower and higher current thresholds Ig1 and Ig2 is set to satisfy a relationship of X1<X2<Y1<X3<Y2<X4<Y3<X5<Y4< - - - <Xn<Yn−1. Each of the n thresholds X1 to Xn and n−1 thresholds Y1 to Yn−1 further indicates a threshold of an airflow amount corresponding to each of the output timing values.

When starting up blower 26, control section 10 a operates in the first control mode. In an initial state that no dust is trapped on filter 27, the output timing value U1 is set so that an airflow amount generated by the blower 26 corresponding to an applied power to blower 26 exceeds a value Q0 indicated on the abscissa axis in FIG. 6. In this embodiment, for example, the operating state of blower 26 is indicated by the point A in FIG. 6.

When cleaning operation is conducted from the initial state, cleaner 20 starts separating dust from airflow and thus dust is collected or trapped on filter 27. As the cleaning operation proceeds, the collected dust is increased, resulting in increase in the airflow-resistance of the filter 27. Thus, the intake airflow amount of blower 26 is decreased. In response to these processes, the applied power to blower 26 gradually decreases from the operating point A along the line in FIG. 6. This is because that the load bearing on blower 26 reduces and a current In flowing through motor 5 also decreases.

When the current value In goes lower than the threshold X1 of the lower limited current threshold, control section 10 a changes the output timing value from U1 to U2 to shorten the output timing ta of the control signal to bidirectional thyristor 2 with reference to the zero-cross point and causes the conducting angle Φ of bi-directional thyristor 2 to increase. Increase of the conducting angle Φ causes the applied power to blower 26 to increase, resulting in increase of the intake airflow amount of blower 26.

After that, as the collected dust increases in the operation in which the output timing ta is kept U2, the airflow-resistance of filter 27 further increases and the intake airflow amount of blower 26 further decrease again. In accordance with decrease of the intake airflow amount, the current value In flowing through motor 5 gradually decreases.

When the current value In goes lower than the threshold X2 of the lower limited current threshold, control section 10 a changes the output timing value from U2 to U3 to further shorten the output timing ta with reference to the zero-cross point so that the conducting angle Φ of bidirectional thyristor 2 further increases. Increase of the conducting angle causes the applied power to blower 26 to further increase, resulting in increase of the intake airflow amount of blower 26.

As aforementioned above, while collection of dust on filter 27 proceeds, control section 10 a changes the output timing value in order of U1, U2, U3, U4, - - - Un every time that the current In goes smaller than the respective thresholds X1, X2, X3, X4, - - - Xn of the lower limited current thresholds. Control section 10 a restrains decrease of the intake airflow amount of blower 26 by changing the output timing value.

In the control method set forth above, the control is carried out assuming that, as an amount of dust trapped on filter 27 increases, an airflow-resistance increases resulting in decrease of the applied power to blower 26. On the other hand, when an operator actually uses cleaner 20, variation in a positional relationship a gap between floor brush 35 and floor surface, variation in a bending angle airflow pass in diameter of a flexible cylindrical hose 30, or uneven accumulation of a collected dust within filter 27 may cause an airflow-resistance to tentatively decrease and an intake airflow amount to unexpectedly increase.

In case that the intake airflow amount is unexpectedly changed when the operating point of blower 26 is positioned, for example, at B in FIG. 6 or the output timing value is being U4, control section 10 a changes the output timing value from U4 to U3 if the current value In exceeds the threshold Y3 of the higher limited current threshold. Such change of the output timing causes the conducting angle Φ of bi-directional thyristor 2 to decrease and the applied power to blower 26 to decrease. At this moment, the applied power to blower 26 is also decreased. Therefore, control section 10 a restrains an abrupt increase of the intake airflow amount of blower 26.

Inventors of the present invention experimentally confirmed the number of values of each item, i.e., output timing value, lower and higher limited current thresholds Ig1, Ig2, which is required when the control section 10 a carries out the control operation to restrain the variation in the airflow amount in the first control mode. For example, in case that the upper limit value of the applied power of the blower 26 was one (1) kW and the applied power of the range within 700 W and 950 W was applied to the blower 26, the number of the output timing values and lower and higher limited current thresholds Ig1 and Ig2 were at most 10, respectively. Therefore, a required precise control in the first control mode can be achieved when 10 of the output timing values, the lower limited current thresholds Ig1 and the higher limited current thresholds Ig2 are respectively prepared beforehand.

Inventors of the present invention further confirmed the number of values of each item, i.e., output timing value, lower and higher limited current thresholds Ig1, Ig2, which is additionally required in order that the control section 10 a adjusts the applied power to the blower 26 to the upper limit value (1 kW) in the first control mode. The additional number of the output timing values and lower and higher limited current thresholds Ig1 and Ig2 were 50 to 100, respectively.

As described above, a memory having a large capacity is needed to carry out a control operation in the first control mode alone in which variation in the airflow amount of the blower 26 is restrained when the applied power to the blower 26 is within a prescribed range and the applied power is adjusted to the upper limit value (target value) when the applied power exceeds the prescribed range. This is because that it is required to narrow the dividing or sampling intervals of each item, i.e., output timing, lower and higher limited current thresholds Ig1, Ig2, within a control range to achieve the above-described control operation, resulting in such a large amount of values of each item needed.

Therefore, to dissolve the above-described problem, another control mode (second control mode) is needed together with the first control mode. Second control mode which is suitable to control the blower 26 in the vicinity of the upper limit value of the applied power to the blower 26 will be described.

In the second control mode, control section 10 a calculates an error ΔI between a current value In detected by current detecting section 3 and a targeted current value Is (hereinafter referred to as “target current Is”) by the formula (ΔI=Is-In). The target current Is indicates a value determined experimentally based on an higher limited value of an applied power to blower 26 and is stored in memory 8 previously. Control section 10 a determines an output timing ta of a control signal to bidirectional thyristor 2 based on the error ΔI. An instruction value Tp of the output timing ta of the control signal is calculated by control section 10 a, for example, by the following formula: Tp=Tp′+α×ΔI  (1)

Wherein Tp′ is the last time instruction value and a is a coefficient.

The above-described second control mode is a target value control that exclusively aims at a control operation which adjusts the current In to the target current Is. Control section 10 a operating in the second mode can adjust the applied power to the blower 26 to a prescribed target value. The target current Is is previously set as a value corresponding to the higher limited value (1 kW) of the applied power to blower 26.

While operating in the second control mode, if an airflow-resistance is further increased because of increase of the amount of collected dust in filter 27 and operation under the higher limited value of the applied power is continued, motor 5 may become malfunction. To prevent this, control section 10 a changes the output timing of the control signal to make the applied power decrease, and outputs an informing signal to informing section 40 so as to call an operator's attention to the filter 27 packed with dust. Thus, the operator can promptly eliminate dust out of the filter 27.

A process for determining output timing ta will be described with reference to a flowchart shown in FIG. 7. Control section 10 a periodically conducts the process according to a control program previously installed in memory 8.

In step S1, current acquiring section 71 acquires a current value In detected by current detecting section 3. In step S2, control mode selecting section 73 determines whether the present control mode is the first control mode. If the present control mode is the first control mode, step S3 is taken. In step S3, output timing determination section 54 compares the detected current In to the lower and higher current thresholds listed in FIG. 5. For example, when the present output timing value is being set to U4, control section 10 a checks whether or not the detected current In falls within a range from X4 to Y3 (X4≦In<Y3). If the detected current In falls within the above range, output timing determination section 54 maintains the present output timing value U4 in step S5. On the other hand, in step S3, if the detected current In falls out the above range, step S4 is taken. Output timing determination section 54 changes the present output timing value U4 to the upper value U5 or lower value U3 of the table in FIG. 5 and thus output timing value is determined as U4 or U5 in step 5. In step S2, if the present control mode is the second control mode, step S6 is taken and output timing determination section 54, calculates instruction value Tp by the formula (1). Following the calculation, output timing value of control signal is determined as the calculated value in step S5.

A condition that control section 10 a changes its control mode from the first control mode to the second control mode will be described. In control section 10 a, an output timing value Un shown in the table in FIG. 5 is previously set as an output timing ta for switching the first control mode to the second. In an operation that control section 10 a controls blower 26 under an output timing value Un in the first control mode, control mode selecting section 73 switches the present control mode (the first control mode) to the second when it is determined that the detected current In goes smaller than lower limited current threshold Xn (In<Xn). The lower limited current threshold Xn forms a first switching threshold to switch the first control mode to the second.

Next, a method of switching the second control mode to the first control mode under some switching conditions will be described.

-   Switching conditions include:

Condition 1: Using a detected current In,

Condition 2: Using an output timing instruction value Tp and

Condition 3: Using a detected current value In and an output timing instruction value Ta.

In case that condition 1 is adopted as the switching condition, control section 10 a switches the present control mode (second control mode) to the first control mode when the detected current In exceeds a prescribed switching threshold previously stored in memory 8.

In case that condition 2 is adopted, control section 10 a switches the present control mode (second control mode) to the first control mode when the output timing instruction value Tp calculated by the formula (1) exceeds an output timing threshold Tw previously stored in memory 8.

Further, in case that condition 3 is adopted, control section 10 a switches the present control mode (second control mode) to the first control mode when the output timing instruction value Tp calculated by the formula (1) exceeds an output timing threshold Tw previously stored in memory 8 and furthermore an error ΔI between a detected current In and the target current Is goes smaller than an error threshold ΔIq (ΔI<ΔIq ) previously stored in memory 8. Control section 10 a may adopt the above-described conditions alone or in combination.

As described above, controller 100 of cleaner 20 in this embodiment can control the operation by switching the control mode from the first control mode in which a variation of airflow is restrained irrespective of an amount of collected or trapped dust by the filter to maintain the suction power of the cleaner, to the second control mode in which the applied power to blower 26 is controlled to adjust the applied power to a targeted power, and vice versa.

To be more precise, in controller 100 of cleaner 20, control section 10 a operates in the first control mode when an applied power is equal to or less than a prescribed value, e.g., 950 W, and in the second control mode when the applied power exceeds 950 W. In the second control mode, the applied power is to be maintained at 1 kW. Controller 100 as described above operates in the first control mode to restrain variation in the airflow amount of blower 26 by regulating the applied power itself to blower 26 in such state that an amount of collected or trapped dust in filter 27 is small and thus a sufficient suction power can be achieved even if the applied power to blower 26 is small. Thus, the cleaner 20 being operated in the first control mode can maintain a stable cleaning ability without consuming an excess power. After that, controller 100 then operates in the second control mode to adjust the applied power to blower 16 to an upper limit value of the applied power which is provided by law when an amount of collected dust in filter 27 increases and the applied power to blower 26 approaches to the upper limit value. Thus, the cleaner 20 can rapidly increase its suction power with a simple configuration when dust is further collected or trapped by filter 27.

In the second control mode, control section 10 a controls the applied power to blower 26 to meet the targeted power value, calculating the instruction value Tp of output timing of control signal using the rate α, the detected current value In and the targeted current value Is. Accordingly, comparing to the operation in the first control mode, the operation in the second control mode can adjust the applied power to blower to the targeted value without requiring the number of constants, e.g. output timing values, current threshold values and so on, in excess. The operation in the second control mode is effective.

The method for switching the first control mode to the second does not need a lot of process load to microprocessor 7 and realize high process speed for the switch of the mode, since the method simply use the detected current In and does not require newly complicated process to switch the mode.

The method for changing the second control mode to the first also does not need a lot of process load to microprocessor 7 and realize high process speed for the switch of the mode, since the method simply use the detected current In and the instruction value Tp calculated by the formula (1).

Control section 10 a conducts its mode selection using the detected current In and thus blower 26 is instantly controlled even if a variation of airflow resistance takes place due to increase of the collected dust in filter 27, variation of positional relationship between floor brush 35 and floor surface, variation in bending angle of a flexible cylindrical hose 30, or uneven accumulation of the collected dust within filter 27. This is because that the detected current In can be treated to be equivalent to both the applied power to blower or the intake airflow amount which are varied by the above-described incidents.

SECOND EMBODIMENT

In the first embodiment, the control section 10 a controls blower 26 by using the detected current In as it is. In the second embodiment, the control section 10 b controls blower 26 by using a calculated current value Ix which results from calculation in a method that is predetermined taking a relationship between the detected current In and the applied power into account every time when the detected current In is acquired. The calculation does not need a complicated process, and thus not adversely affect the processing capacity of a microprocessor.

With reference to FIG. 8, respective functions of control section 10 b controlling blower 26 based on the calculated current value Ix (hereinafter referred to as “calculated current Ix”) are described. Control section 10 b is formed such that a current calculating section 72 is added to control section 10 a shown in FIG. 4.

Current acquiring section 71 acquires the detected current In, which is periodically detected by current detecting section 3 in a predetermined period, flowing through motor 5 and the detected current In is input to current calculating section 72. Current calculating section 72 calculates according to a predetermined method to obtain the calculated current Ix. The calculated current Ix is set to vary in response to a variation of an applied power to blower 26. After calculation, current calculating section 71 outputs the calculated current Ix to both control mode selecting section 73 and output timing determination section 54. Control mode selecting section 73 checks its present control mode, and changes the control mode if needed. In accordance with the calculated current Ix and the checking result of control mode selecting section 73, the output timing determination section 54 determines output timing ta of control signal to bidirectional thyristor 2.

An example in which a calculated current Ix is obtained based on a detected current In is explained. Current acquiring section 71 periodically acquires, for example, the detected current In every 0.2 millisecond on commercial power with 50 Hz. In other words, the detected current In is acquired 100 times in one period, i.e., 20 millisecond, on the commercial power. The calculated current Ix (=Σ In) is obtained by reiteratedly adding one detected current In acquired to the calculated result. Where a period of the Σ In (calculated current Ix) is made to a period of the commercial power, 100 times of the detected current In are added. The calculated current Ix varies in response to a variation of the applied power to blower 26 according to a variation in the intake airflow amount.

Even if noise of the commercial power adversely affects the detected current In when sampling at a certain timing, calculated current Ix can still be used because the calculated current Ix is obtained by addition of the sampled currents and thus such affection by noise is effectively alleviated. Hence the applied power to blower 26 can be accurately and reliably controlled. Alternatively, it can be possible that the detected current In is modified by multiplying the detected current In by a weighting ratio (β) every time the detected current In is acquired and the modified current In is added successively.

In this embodiment, in place of the detected current In it is possible to apply the calculated current value Ix obtained therefrom.

In these embodiments aforementioned, output timing determination section 54 acquires both the output timing value at the present time and the current threshold value Ig1 or Ig2 on the data table stored in memory 8 as indicated in FIG. 5. The present invention is not necessarily limited to using the data table. Instead of the preset data table, output timing determination section 54 may be configured to calculate lower limited current threshold of n-th value (Xn) according to the following formula: Xn=X1+K×(n−1)×(output timing value)  (2) wherein X1 indicates lower limited current threshold of the first value and K indicates a proportional rate experimentally predetermined.

Intervals (ΔUn) of respective adjacent output timing values (Un) and (U(n−1)) and intervals (ΔXn) or (ΔYn) of respective adjacent current threshold values (Xn) and (X(n−1)) or (Yn) and (Y(n−1)) are not needed to be constant and may be set in accordance with intended use of cleaner 20 or characteristic of blower 26.

THIRD EMBODIMENT

With reference to FIGS. 9 to 11, controller 110 of cleaner 20 in the third embodiment is now described. A DC power source 61, e.g., secondary battery, powers controller 110 to rotate motor 5 as shown in FIG. 9. Motor 5 is connected in series with the applied power to the motor 5.

As shown in FIG. 11, control section 10 c includes output timing determination section 64 provided with a PWM signal generating section 65 generating a pulse width modulation signal. The PWM signal can be generated by publicly known method. When power voltage from DC power source 61 is applied to controller 110 and the PWM signal formed with a period having Pc second, as indicated in FIG. 10(b), is supplied to a gate of MOSFET, motor 5 is periodically switched on for tc second to rotate. Duty factor Du of the PWM signal is calculated as follows: Du=tc/Pc  (3) As can be understood from the formula, larger the duty factor Du larger the applied power to blower 26.

As described above, control section 10 c can change the output timing of the control signal to MOSFET 62, varying the duty factor Du of PWM signal from the PWM signal generating section 65. In the controller 110, the duty factor Du is referred as an output timing and thus, the output timing value shown in FIG. 5 and the instruction value of output timing calculated by the formula (1) are needed to be set taking the duty factor Du into consideration.

It should be noted that not only a commutator motor but also a brushless DC motor may be applied to form blower 26 in controller 110.

FOURTH EMBODIMENT

An electric vacuum cleaner in forth embodiment is now described. The cleaner of this embodiment includes a fixed type cleaner installed such as between walls, on a ceiling, on a roof, or under a floor and a central cleaner having one filter and a plurality of airflow intakes being in fluid communication with the filter. A relationship between airflow amount of blower 26 and the applied power during the operation is, for example, illustrated in FIG. 12. Comparing to a canister type cleaner, the cleaner of this type requires larger applied power to blower 26 and is continuously operated for relatively a long time once the operation is started. Therefore, an idling operation for the blower is required before the control operation (ordinary operation) is effected.

Control section 10 c outputs an informing signal to informing section 40 when the second control mode is effected so that a light emitting element is flickered to indicate an operational state of the second control mode to an operator. Flickering of the light emitting element informs an operator that an amount of dust trapped on the filter approaches an allowable level before the amount of dust exceeds the allowable level. No specific threshold value for informing full of dust on the filter is needed.

FIFTH EMBODIMENT

Fifth embodiment is now described. Electric vacuum cleaners described in the above first to fourth embodiments use a current detecting section to detect an airflow amount. In this embodiment, however, in lieu of the current detecting section air pressure detecting section 81 is provided in controller 110 to detect the airflow amount as illustrated in FIG. 13.

Air pressure detecting section 81 detects air pressure generated by airflow that varies in response to the amount of dust trapped on the filter 27. Specifically the detection of the air pressure is implemented between an air intake and filter 27. Control section 10 d in this embodiment includes memory 8 storing a data table similar to the data table illustrated in FIG. 5. In the data table of this embodiment, a lower and higher limited pressure thresholds respectively corresponding to output timings are used instead of a lower and higher limited current thresholds in FIG. 5. Control of blower 26 in the first control mode and switch from the first control mode to the second are performed according to an output from air pressure detecting section 81. Control of blower 26 in the second control mode and switch from the second control mode to the first control mode as well as other operations are like operations described in the first to fourth embodiments.

In the above descriptions of respective control sections 10 a, 10 b, and 10 c, processes of current acquiring section 71, current calculating section 72, control mode selecting section 73, and output timing determination section 54 are realized with software. It may be possible however to realize such processes or functions with hardware configuration.

The present invention has been described with respect to specific embodiments. However, other embodiments based on the principles of the present invention should be obvious to those of ordinary skill in the art. Such embodiments are intended to be covered by the claims. 

1. An electric vacuum cleaner comprising: a blower for generating an air flow containing dust; a filter configured to separate dust from the air flow; a switching element for switching a current flowing through the blower in response to a control signal; an air-flow-amount sensing section for sensing an amount of the air flowing through the filter to output a first value indicating the sensed result, the air-flow-amount being varied in response to amount of the dust separated by the filter; a current detecting section for detecting a current flowing through the blower to output a second value indicating the detected current value, the current corresponding to power applied to the blower; and a control section for selecting, in accordance with power applied to the blower, one of a first control mode in which a suitable output timing of the control signal from the control section to the switching element is determined so that variation in the amount of the air flow is restrained based on the first value and a second control mode in which a suitable output timing of the control signal is determined so that the applied power to the blower is maintained at a prescribed target value based on the second value and for controlling the operation of the switching element with the control signal outputted at the suitable output timing of the selected mode.
 2. The electric vacuum cleaner according to claim 1, wherein the air-flow-amount sensing section includes a current sensor for sensing a current flowing through the blower, the current being varied in response to an amount of the air flowing through the filter.
 3. The electric vacuum cleaner according to claim 1, wherein the control section selects the first control mode when the power applied to the blower is equal to or less than a prescribed value and otherwise selects the second mode.
 4. The electric vacuum cleaner according to claim 1, further comprising a zero-cross detecting section for detecting a zero-cross point of the applied voltage to the blower, wherein the control section outputs the control signal every half period of the applied voltage with reference to the detected zero-cross point.
 5. The electric vacuum cleaner according to claim 1, wherein the control section includes a PWM (pulse-width-modulation) signal generation section for outputting a PWM signal to the switching element as the control signal.
 6. The electric vacuum cleaner according to claim 1, further comprising a memory for storing a plurality of output timing values and thresholds of the air-flow-amount corresponding to each value of the output timing values, wherein, in the first control mode, the control section compares the thresholds with one of the first value and a value calculated based on the first value, selects one of the plurality of output timing values in accordance with the compared result, and outputs the control signal based on the selected value of the output timing.
 7. The electric vacuum cleaner according to claim 6, wherein the memory stores a first switching threshold, and wherein the control section switches the first control mode to the second control mode when the one of the first value and the calculated value exceeds the first switching threshold.
 8. The electric vacuum cleaner according to claim 1, further comprising a memory for storing value of a target current and a proportional coefficient, wherein the control section, in the second control mode, calculates an error between the target current value and one of the second value and a current value calculated based on the second value, and determines the suitable output timing according to a value that is obtained by multiplying the error by the proportional coefficient.
 9. The electric vacuum cleaner according to claim 8, wherein the memory stores a second switching threshold, and wherein the control section switches the second control mode to the first control mode when the error goes smaller than the second switching threshold.
 10. The electric vacuum cleaner according to claim 1, further comprising an informing section for informing that the blower operates in the second mode. 